1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine or a printer which employs an electrostatic recording process, an electrophotographic recording process, and the like. More specifically, the present invention relates to an image forming apparatus in which air is blown onto a lower surface of a recording material when the recording material on which a toner image is heat fixed is discharged.
2. Related Background Art
Conventionally, there is known an image forming apparatus in which the recording material is cooled immediately after passing through a conveyance roller in order to prevent a malfunction from occurring in the image forming apparatus due to heat applied to the recording material which has been subjected to heat fixing by a fixing unit.
In FIG. 11, the image forming apparatus of this kind is shown. As shown in FIG. 11, a recording material S on which a toner image is fixed by a fixing unit 300 and whose temperature is high is discharged to a sheet discharging section 150 after passing through a pair of conveyance rollers 130 and 140, and the recording material S receives the air from a blowing unit 200 immediately after passing through the pair of conveyance rollers 130 and 140.
As a result, it is possible to cool the recording material S, making it possible to prevent plastic films such as overhead transparency (OHT) sheets from adhering to one another in the sheet discharging section 150 due to high temperature. Further, by cooling the recording material S, it is possible to prevent such an adverse affect that the temperature of the sheet discharging section 150 is raised so high to adversely affect the temperature inside an image forming apparatus 500. Further, in a case where the image forming apparatus 500 is capable of forming an image on both sides of the recording material S, it is possible to cool the both sides of the recording material S one side at a time, thereby making it possible to prevent the temperature inside the image forming apparatus 500 from rising and to form a high quality image on the recording material S.
Incidentally, there is a case where the entire recording material S is curled in the sheet discharging section 150 to be turned over when the recording material S is discharged from the pair of conveyance rollers 130 and 140. In order to prevent this, a configuration can be thought in which the conveyance roller 130 and the conveyance roller 140 are disposed alternately as shown in FIG. 12 to add stiffness to the recording material S by making the recording material S to be rippled, thereby discharging the recording material S straight.
However, in this case, when the air from the blowing unit 200 is blown onto the recording material S being conveyed, it is possible to lower the temperature of the recording material S, however, there occurs such a phenomenon that the recording material outputted finally is slightly rippled. This phenomenon is especially remarkable in a case of the recording material made of plastic film such as an OHT sheet. This is deemed to occur because the OHT sheet rippled at the high temperature is cooled as it is to remain in the rippled shape.
In this regard, in order to solve the problem of the rippling, there are disposed through rollers of the pair of conveyance rollers which are straight and continuous in a longitudinal direction. Further, in order to prevent the above-mentioned curl (turning over) of the recording material in the sheet discharging, a blowing unit is disposed by which it is possible to bring the recording material upward to convey the recording material by the air blown from the blowing unit.
As a result, it is possible to prevent the rippling and curl of the recording material at the same time.
However, in the above image forming apparatus, stacking capability of the recording material is slightly deteriorated because the air in an amount large enough to bring the recording material being conveyed upward is always blown onto the recording material, although it is a minor problem. This is because the air may impart too much ascending force to the recording material. More specifically, as shown in FIG. 13A, when a trailing edge of the recording material passes through a pair of conveyance rollers 131 and 141 and falls into the sheet discharging section due to a dead weight of the recording material, the air from the blowing unit serves as a resistance, so a falling movement of the trailing edge of the recording material is not stabled. As a result, as shown in FIG. 13B, stacking alignment and stacking capability of the recording material are deteriorated.
Further, depending on a kind of the recording material, the leading edge portion of the recording material is cooled and solidified in a state where the leading edge portion of the recording material is suspended from the pair of conveyance rollers 131 and 141, thereby causing the curl in the leading edge portion of the recording material.
In addition, when the stiffness of the recording material is varied in accordance with the environment, conveyance capability of the recording material may be deteriorated.